Thermodynamics, Statistical Physics, and Quantum Mechanics

131

where is the Langevin function. For we can

expand (S.4.36.3) to obtain

Since and

we have for thedielectric constant

4.37 Two-Dipole Interaction (Princeton)

Introducesphericalcoordinates with the axis along theline of thesepa-

rationbetween the dipoles.Then the partitionfunctionreads

The potential energy of the interaction can berewritten in the form

Since

(S.4.37.2)becomes

THERMODYNAMICS AND STATISTICAL PHYSICS